The present invention relates to a safety device for a machine having a first machine part that performs a working movement towards a second machine part.
A known method of processing workpieces in a non-cutting manner is to bend workpieces or bend the edges of workpieces. In so doing, an initially flat workpiece is reshaped under pressure in the region of the processing site. In the case of machine processing, machines used for this purpose are referred to generally as press brake. However, the invention is not limited to press brake machines in the narrower sense and can likewise be used in edge-press brake machines, stamping machines, cutting machines and other machines in which two machine parts perform a dangerous working movement towards each other and in which in order to avoid accidents a protective device is provided that moves simultaneously and acts in a non-contact manner.
In the case of press brake machines, shaping of the workpiece is performed substantially by virtue of the fact that the workpiece is pressed against a die using a bending punch. A desired shaping is achieved by a corresponding design of the bending punch and the die. The bending punch is often a tool that is arranged in a movable upper tool-carrier, whereas the die sits on a fixed lower tool-carrier. However, since it concerns only the relative movement of the two tool-carriers, as an alternative, the die can also be moved, or the two tool-carriers can be moved towards each other. The safety device in accordance with the invention can be used in all these cases.
It is easy to comprehend that operating personnel are exposed to considerable risk when using a press brake machine, in particular to the risk of squashing or even amputating body parts. Accordingly, it has been known for a long time to provide press brake machines and the like with a safety device in order to avoid accidents as far as possible.
The prior art discloses a multitude of proposals for protective devices for press brakes and similar machines. Many proposals focus on the task of making safe the danger zone at the leading edge of the moving machine part as good as possible, in particular to reliably recognize dangerous encroachments into the working movement of the machine from different directions and/or in different operating situations. Numerous proposals, such as in U.S. Pat. No. 5,579,884, relate to arranging a plurality of optical barriers/light beams in the region of the leading edge of the moving machine part. As soon as at least one of these light beams in the working movement of the machine part is interrupted, an output signal is generated that stops the working movement of the machine.
There are also proposals to achieve a plurality of optical barriers using a camera on the receiving side, for example in DE 10 2004 058 472 A1. The camera is in this case illuminated over the entire area using a “large” light beam. Only selected pixel regions on the camera sensor are monitored and evaluated. These pixel regions trigger a switch-off signal if a shadow covers the light beam on the pixel region.
EP 1 674 785 B1 describes a camera-based safety device for making safe a press brake machine. Several different protective fields are illustrated. In addition to extremely small protective fields that amount to less than 10% of the total area of the field of view of the receiving device, large-area protective fields are also illustrated. In one embodiment, a large-area protective field comprises a plurality of unconnected, line-shaped segments. The line-shaped segments are arranged in parallel with the plane of movement defined by the leading edge.
In all cases, the question arises as to how dangerous encroachments into the movement path of a press tool can be reliably recognized without triggering unnecessary false alarms, the latter having an adverse effect on the productivity of the machine. In addition, it is also desired that a dangerous encroachment be recognized as quickly as possible in order to be able to switch off the machine quickly in the event of a danger. In so doing, all optical barriers and/or protective field geometries are a compromise in the protective field between the requirements of the working rate, the reliability of error recognition, the avoidance of false alarms and the production costs. Despite the numerous already known proposals, there is also the desire to provide a safety device that fulfills the conflicting requirements in the most optimum manner possible.
In addition, there is a desire to maintain the protective field until the end of the working movement, so that the machine operator is protected until the very end of the working movement. However, a problem arises in this case, because the leading safety barrier will already be interrupted by the second machine part and/or by the workpiece before the working movement is completed. The optical safety barriers must therefore be deactivated at the end of the working movement. This intentional deactivation is known as ‘muting’. Without muting, the first machine part could not complete its working movement, since it would be switched off prematurely by the safety device.
DE 103 53 353 A1 discloses a camera-based safety device in which the entire area of the protective field is monitored and continuously reduced at the end of the working movement. However, such an approach requires a high level of computing capacity with the result that the costs for the practical implementation are high.
EP 1 387 121 B1 discloses a safety device having a plurality of individual optical safety barriers that are deactivated in sequence at the end of the working movement. Consequently, this known safety device makes it possible to provide a certain amount of protection of the operator until the completion of the working movement. However, the amount of protection is not yet optimum, since the number and the distribution of the safety barriers allows only rather rough steps when adjusting the protective field. In the moment in which an optical safety barrier is deactivated, the protective field being spanned “jumps” upwards and leaves a gap at the workpiece which is only re-closed with the further working movement of the first machine part.